Distinguish between unpolarized light and linearly polarized light. How does one get the linearly polarised light with the help of a polar?
In a beam of unpolarized light, the vibrations of light vectors are in all directions in a plane perpendicular to the direction of propagation. 
In the linearly polarised light, the vibrations of light take place in a particular direction, perpendicular to the direction of wave motion.
Polarized light can be distinguished, from unpolarized light, when it is allowed to pass through a Polaroid. Polarized light does can show the change in its intensity, on passing through a Polaroid; intensity remains same in case of unpolarized light.
When the unpolarised light wave is incident on a polaroid, then the electric vectors along the direction of its aligned molecules, get absorbed; the electric vector, oscillating along a direction perpendicular to the aligned molecules, pass through. This light is called linearly polarized light.
